Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Liquidation Basis of Accounting [Member] - USD ($) $ in Thousands	Mar. 31, 2016	Mar. 31, 2015
LIABILITIES
Liquidating distributions payable	$ 6,213	$ 7,714
Fair Value, Measurements, Recurring [Member]
ASSETS
Total Assets	662,958	968,071
LIABILITIES
Liquidating distributions payable	6,213	7,714
Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member] | Money Market Funds [Member]
ASSETS
Total Assets	1,835	19,150
Fair Value, Measurements, Recurring [Member] | Marketable Securities [Member] | U.S. Treasury Bills [Member]
ASSETS
Total Assets	655,121
Fair Value, Measurements, Recurring [Member] | Marketable Securities [Member] | U.S. Government Agency Securities [Member]
ASSETS
Total Assets	6,002
Fair Value, Measurements, Recurring [Member] | Marketable Securities [Member] | Municipal Commercial Paper and Variable Demand Notes [Member]
ASSETS
Total Assets		12,064
Fair Value, Measurements, Recurring [Member] | Marketable Securities [Member] | Corporate Commercial Paper [Member]
ASSETS
Total Assets		18,880
Fair Value, Measurements, Recurring [Member] | Holdings of New GM Securities [Member] | New GM Common Stock [Member]
ASSETS
Total Assets		427,151
Fair Value, Measurements, Recurring [Member] | Holdings of New GM Securities [Member] | New GM Warrants [Member]
ASSETS
Total Assets		490,826
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
ASSETS
Total Assets	1,835	937,127
LIABILITIES
Liquidating distributions payable	6,213	7,714
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Cash Equivalents [Member] | Money Market Funds [Member]
ASSETS
Total Assets	1,835	19,150
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Holdings of New GM Securities [Member] | New GM Common Stock [Member]
ASSETS
Total Assets		427,151
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Holdings of New GM Securities [Member] | New GM Warrants [Member]
ASSETS
Total Assets		490,826
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
ASSETS
Total Assets	661,123	30,944
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Marketable Securities [Member] | U.S. Treasury Bills [Member]
ASSETS
Total Assets	655,121
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Marketable Securities [Member] | U.S. Government Agency Securities [Member]
ASSETS
Total Assets	$ 6,002
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Marketable Securities [Member] | Municipal Commercial Paper and Variable Demand Notes [Member]
ASSETS
Total Assets		12,064
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Marketable Securities [Member] | Corporate Commercial Paper [Member]
ASSETS
Total Assets		$ 18,880